There are several known ways to anesthetize a patient. One important method for anesthetizing a patient in preparation for, for example, dental, obstetric, gynecological, plastic, orthopedic or other surgery, is to administer a gas to the patient by inhalation. The anesthetic gas passes into the patient's lungs and then into the patient's bloodstream by which it is delivered to the nervous system to perform the anesthetic function.
The most widely used gas employed as an anesthetic is nitrous oxide. This gas is an effective anesthetic and is relatively inexpensive. However, recently, questions have arisen regarding the safety of nitrous oxide. Specifically, it has been reported that nitrous oxide is chemically active and may undergo biotransformation to metabolites that could be toxic, is metabolically active, is a fetal toxin, can cause spontaneous abortions (miscarriages), is a carcinogen and has cardiosuppressive properties. It is commonly used with an induction or co-general anestheic medication for other than dental surgery. This can prolong the period for the patient to recover consciousness following surgery. Nitrous oxide is also a strong oxidizer and can vigorously support combustion if present in sufficient quantity by accident or lack of unawareness in an operatorium, representing a hazard to both the patient and medical staff. Accordingly, it is desirable to be able to carry out anesthesia by patient inhalation without employing nitrous oxide and without significantly increasing the cost of the anesthetic procedure.
Nitrous oxide can inactivate certain enzymes by oxidizing the cobalt in vitamin B12. This can lead to a decrease in serum methionine, which reduces the conversion of uridine to thymidine, one of the four nucleotides of deoxyribonucleic acid (DNA). The overall effect is a decrease in DNA production resulting in the inhibition of cell division. Tissue with a high rate of cell turnover would be most susceptible, possibly explaining the reproductive and carcinogenic problems nitrous oxide can cause.
The fetal toxicity of nitrous oxide raises particular problems. Women may not be aware that they are pregnant in the early stages of pregnancy. The use of nitrous oxide at this stage can have unfortunate consequences including spontaneous abortions, which have been reported. Since all women of childbearing age would be at risk of having nitrous oxide administered in the early stages of a pregnancy, all uses of nitrous oxide on women who are menstruating and/or who are pre-menopause, would require testing prior to use to establish the absence of a pregnancy. This approach is not practiced and the procedure is costly and time consuming and can never be absolutely accurate.
In addition to the concern for patient exposure to nitrous oxide, it has also been noted that medical professionals who work in dental and surgical operatoriums where concentrations of waste nitrous oxide present in the room environment exceed recommendations by federal agencies such as NIOSH, have a higher incidence of spontaneous abortions/miscarriages and fetal malformations than control groups. It has been found that many operatoriums exceed the recommendations.
Accordingly, it is an object of this invention to provide a method for anesthetizing a patient by the patient's inhalation of a gas which does not include nitrous oxide.